Fading of wound-induced volatile release during Populus tremula leaf expansion.

The release of stress-driven volatiles throughout leaf development has been little studied. Therefore, we subjected poplar leaves during their developmental stage (from 2 days to 2 weeks old) to wounding by a single punch hole, and measured online the wound-induced volatile organic compound emissions. Our study shows that the emission of certain volatile compounds fades with increasing leaf age. Among these compounds we found lipoxygenase products (LOX products), acetaldehyde, methyl benzoate, methyl salicylate, and mono- and sesquiterpenes. In parallel, we studied the fading of constitutive emissions of methanol during leaf maturation, as well as the rise in isoprene constitutive emission during leaf maturation and its relationship to leaf photosynthetic capacity. We found highly significant relationships between leaf chlorophyll content, photosynthetic capacity, and leaf size during leaf ageing. As the level of constitutive defences increases with increasing leaf age, the strength of the volatile signal is expected to be gradually reduced. The higher elicitation of volatile organic compound emissions (especially LOX products) in younger leaves could be an evolutionary defence against herbivory, given that younger leaves are usually more subjected to infestation and herbivory.

Emission Timetable and Quantitative Patterns of Wound-Induced Volatiles Across Different Leaf Damage Treatments in Aspen (Populus Tremula).

Plant-feeding herbivores can generate complex patterns of foliar wounding, but it is unclear how wounding-elicited volatile emissions scale with the severity of different wounding types, and there is no common protocol for wounding experiments. We investigated the rapid initial response to wounding damage generated by different numbers of straight cuts and punctures through leaf lamina as well as varying area of lamina squeezing in the temperate deciduous tree Populus tremula. Wounding-induced volatile emission time-courses were continuously recorded by a proton-transfer-reaction time-of-flight mass-spectrometer. After the mechanical wounding, an emission cascade was rapidly elicited resulting in sequential emissions of key stress volatiles methanol, acetaldehyde, and volatiles of the lipoxygenase pathway, collectively constituting more than 97% of the total emission. The maximum emission rates, reached after one to three minutes after wounding, and integrated emissions during the burst were strongly correlated with the severity in all damage treatments. For straight cuts and punch hole treatments, the emissions per cut edge length were constant, indicating a direct proportionality. Our results are useful for screening wounding-dependent emission capacities.

Changes in the first derivatives of leaf reflectance spectra of various plants induced by variations of chlorophyll content.

Reflectance spectra of leaves of winter wheat, maize, sugar beet and wild vine have been measured. Chlorophyll variations induce changes in the first derivatives of the reflectance spectra. A correlation of various derivative indices such as D(725)/D(702), D(lw)/D(sw), D(lw)/D(702), D(725)/D(sw,)D(715)/D(702), D(m)/D(sw), D(m)/D(702) and D(715)/D(sw) with chlorophyll content was tested, when D is the relative height of the first derivative, the subscript numbers give the wavelength in nm for fixed determination and lw, m and sw are the determination in the long-, medium- and short-wavelength maximum, respectively. The short- and long-wavelength maxima are in the range of 690-730 nm, the medium peak is within the other two, in the range of 710-715 nm. Regression models have been obtained for all types of indices and for all studied plant species. The most promising regression model has been selected. This type of model has been similar for maize, sugar beet and wild vine; therefore, a unified regression model is shown to be applicable for chlorophyll estimation in leaves of these species. The regression model for winter wheat was essentially distinct from both individual and unified models for other studied plants. Reasons for the difference in regression models for various species are discussed.